In order to obtain good images with a magnetic resonance imaging apparatus, it is preferable to generate a uniform static magnetic field in the imaging space in which the subject (for example, patient) is placed. Various technologies for correcting non-uniformity in a static magnetic field are known. For example, an approach is known for making the static magnetic field in the imaging space uniform by arranging a ferromagnet, such as an iron shim, in a static magnetic field generated by a static magnetic field magnet. Another example is an approach known in which a shim coil is used. In this approach, the shim coil generates a correction magnetic field for correcting the non-uniformity of a static magnetic field and the correction magnetic field is superimposed on the static magnetic field so that the static magnetic field in the imaging space is uniformized.
As well as making static magnetic fields uniform, there has been a trend in recent years to shorten the shaft length of the static magnetic field magnet of an MRI apparatus so that the subject does not feel claustrophobic and to inhibit an increase of dB/dt (change in the amplitude of the gradient magnetic field per unit of time) caused by an increase in the gradient magnetic field amplitude. This narrows the area that can be imaged along the direction of the body axis. For this reason, when an area wide along the direction of the body axis of a subject is imaged, e.g., when the spine is imaged, the area to be imaged is segmented and imaged while moving the subject in the direction of the body axis.
As described above, when imaging is performed while moving the subject, the anatomy positioned in the imaging space changes. It is known that uniformity of a static magnetic field in an imaging space changes depending on the anatomy positioned in the imaging space. Thus, the above-described correction of non-uniformity of the static magnetic field is performed every time the subject is moved, which sometimes extends the time taken to perform the entire imaging.